U.S. Pat. Nos. 3,706,717 and 3,879,288 disclose the use of vinyl sulfonate/monovinyl compound copolymers as scale inhibitors.
U.S. Pat. No. 4,001,134 discloses the use of maleic anhydride/allyl acetate copolymers as scale inhibitors in sea-water distillation plants.
U.S. Pat. No. 4,253,968 discloses the use of maleic acid/allyl monomer copolymers as cooling water scale inhibitors.
U.S. Pat. No. 4,342,652 discloses the use of maleic acid/allyl sulfonic acid copolymers as scale inhibitors in evaporative desalination units.
U.S. Pat. No. 4,640,793 discloses the use of admixtures containing carboxylic acid/sulfonic acid polymers and phosphonates as scale and corrosion inhibitors.
U.S. Pat. No. 4,166,041 discloses the use of mixtures of polymers prepared from an ethylenically unsaturated dibasic acid and an ethylenically unsaturated sulfonic acid as magnesium hydroxide scale inhibitors in evaporative desalination units. Maleic anhydride/allyl sulfonic acid copolymers are used in these admixtures.
EPO Pat. Applin. No. 84102890.5 discloses copolymers of maleic acid and an adduct of an oxyalkylene and allyl alcohol, and the use thereof for scale inhibition.
U.S. Pat. No. 4,297,237 discloses the use of polymaleic anhydride and polyphosphonates as corrosion inhibitors, and U.S. Pat. Nos. 3,810,834, 3,963,363 and 4,089,796 disclose methods of treating the water of an aqueous system with hydrolyzed polymaleic anhydride to inhibit scale formation.
U.S. Pat. Nos. 2,723,956, 3,289,734, 3,292,152, 3,578,589 and 3,715,307 relate to the use of polymaleic anhydride and copolymers thereof as scale control agents.
U.S. Pat. No. 3,965,027 discloses the use of certain amine adducts of polymaleic anhydride as scale and corrosion inhibitors.
European patent application No. 84301450.7 discloses carboxylic acid/sulfonic acid copolymers in combination with organic phosphonates as scale inhibitors.
However, none of the prior art references described above in any way suggest the efficacy of the instant polymers as calcium scale control agents in systems operating under severe pH and/or calcite saturation levels.
Many commercial waters contain alkaline earth metal cations, such as calcium, barium, magnesium, etc., and anions such as carbonate, sulfate, oxalate and/or phosphate. When the concentrations of these anions and cations are sufficiently high, insoluble reaction products (precipitates) form until the solubility limits are no longer exceeded. These precipitates are alkaline earth metal scales. For example, when the concentrations of calcium ion and any of the above mentioned anions are sufficient to exceed the solubility limitations of the calcium-anion reaction products, a solid phase of calcium scales will form as a precipitate.
Solubility product concentrations are exceeded for various reasons, such as evaporation of the water phase, change in pH, pressure, or temperature, and the introduction of additional ions which can form soluble compounds with the ions already present in the solution. As these reaction products precipitate on heat transfer surfaces in contact with aqueous systems, they form scale. The scale prevents effective heat transfer, interferes with fluid flow, facilitates corrosive processes, and harbors bacteria. Scale is an expensive problem in many industrial water systems, causing delays and shut downs for cleaning and removal. Alkaline earth metal scales commonly form on the metallic surfaces of apparatuses used for thermal treatment of aqueous solutions and suspensions. By alkaline earth metal scales, we mean scale including but not limited to calcium carbonate, calcium oxalate, magnesium oxalate, calcium phosphate, and calcium sulfate. These scales frequently form in the tubes of heat exchangers and on other heat exchange surfaces.
In the past, alkaline earth metal scale inhibition has been facilitated by the use of anionic polyelectrolytes such as polyacrylates, polymaleic anhydrides, copolymers of acrylates and sulfonates, and polymers of sulfonated styrenes and/or by the use of organo-phosphonates, such as hydroxyethylidene diphosphonic acid (HEDP) and aminotrimethylene phosphonic acid (AMP). However, these traditional scale inhibitors are ineffective or less effective in highly alkaline water. For example, HEDP is ineffective because it reacts with calcium at high pH's to form a calcium/phosphonate scale. Due to the difficulty in controlling alkaline earth metal scale under high pH and/or alkalinity conditions, operators generally add acid to lower the pH and consume alkalinity to prevent scaling. The handling of corrosive acid is dangerous and the maintenance of a desired pH may be difficult.
In recent years, increasing the cycles of concentration in industrial cooling towers has become important, especially in the regions where the water supply is limited. Higher cycles correspond to higher concentrations of scale forming elements. With the elimination of acid feed, the higher pH's generated bring a cooling system to high saturation levels more rapidly.
Accordingly, the need exists for an inexpensive, efficient method and polymer or polymer composition for preventing the formation of deposits on metallic surfaces in contact with water by inhibiting the formation of scale and/or by dispersing scale-forming compounds. This need is especially critical in systems which operate under severe pH and/or calcite saturation conditions.
The instant inventors have discovered a method for controlling scale deposition and/or dispersing scale-forming compounds in aqueous systems which operate under severe pH and/or calcite saturation conditions using maleic acid/allyl sulfonate polymers. While such polymers alone are effective inhibitors, other conventional scale and/or corrosion inhibitors may enhance their performance under certain conditions.
The instant polymers are especially effective as agents for controlling calcium carbonate under high pH/high calcite saturation conditions.